From f86a71dfbf35b36b1ce439f65dfe51f591688393 Mon Sep 17 00:00:00 2001
From: Amy Kwan <amy.kwan1@ibm.com>
Date: Sat, 8 Mar 2025 00:23:46 -0500
Subject: [PATCH] [AIX] Ignore linting on repr(C) structs with repr(packed) or
 repr(align(n))

This PR updates the lint added in 9b40bd7 to ignore repr(C) structs that also
have repr(packed) or repr(align(n)).

As these representations can be modifiers on repr(C), it is assumed that users
that add these should know what they are doing, and thus the the lint should not
warn on the respective structs. For example, for the time being, using
repr(packed) and manually padding a repr(C) struct can be done to correctly
align struct members on AIX.
---
 compiler/rustc_lint/src/types.rs         |  6 ++++++
 tests/ui/layout/reprc-power-alignment.rs | 26 +++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index fcadbfc3c4a7e..71116d0bfe42b 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1638,6 +1638,9 @@ impl ImproperCTypesDefinitions {
             return true;
         } else if let Adt(adt_def, _) = ty.kind()
             && adt_def.is_struct()
+            && adt_def.repr().c()
+            && !adt_def.repr().packed()
+            && adt_def.repr().align.is_none()
         {
             let struct_variant = adt_def.variant(VariantIdx::ZERO);
             // Within a nested struct, all fields are examined to correctly
@@ -1659,8 +1662,11 @@ impl ImproperCTypesDefinitions {
         item: &'tcx hir::Item<'tcx>,
     ) {
         let adt_def = cx.tcx.adt_def(item.owner_id.to_def_id());
+        // repr(C) structs also with packed or aligned representation
+        // should be ignored.
         if adt_def.repr().c()
             && !adt_def.repr().packed()
+            && adt_def.repr().align.is_none()
             && cx.tcx.sess.target.os == "aix"
             && !adt_def.all_fields().next().is_none()
         {
diff --git a/tests/ui/layout/reprc-power-alignment.rs b/tests/ui/layout/reprc-power-alignment.rs
index f6c1df55988ba..f144094d43fbc 100644
--- a/tests/ui/layout/reprc-power-alignment.rs
+++ b/tests/ui/layout/reprc-power-alignment.rs
@@ -148,5 +148,29 @@ pub struct I {
     d: f32,
     e: f64,
 }
-
+#[repr(C)]
+pub struct J {
+    a: u8,
+    b: I,
+}
+// The lint also ignores diagnosing #[repr(align(n))].
+#[repr(C, align(8))]
+pub struct K {
+    a: u8,
+    b: u8,
+    c: f64,
+    d: f32,
+    e: f64,
+}
+#[repr(C)]
+pub struct L {
+    a: u8,
+    b: K,
+}
+#[repr(C, align(8))]
+pub struct M {
+    a: u8,
+    b: K,
+    c: L,
+}
 fn main() { }